抄録
1. Large excess of Schiff reagent enhances the color development of the Feulgen reaction in vitro, but this is rather due to the excess of metabisulfite contained in the reagent. The course of the color development is considerably influenced by the composition of the reaction mixture.
2. On the basis of these findings, a standard procedure of the reaction was proposed. This employs 0.1M glycine buffer of pH 2.28 fortified with excess metabisulfite as the medium; then, the volume of the Schiff reagent to be added can be reduced down to 5 per cent of the final volume of the reaction mixture without affecting the sensitivity of the reagent.
3. The attainable maximum of the color intensity is conditioned by the method of hydrolysis; N HCl at 60° gives higher values than glycine buffers of pH 1.42 or 2.28 at 100° The observed difference is not necessarily due to the destruction of the potentially reactive group. Hydrolysis for 15-30 minutes with N HCl at 60° gives an extinction value of ca. 0.25 (1cm optical path) per μg DNA-P per ml of the final mixture prepared in accordance with the standard procedure, after standing for 3-4 hours.
4. The spectral absorption curve of the Feulgen pigment is modified by the conditions of hydrolysis and the temperature and duration of the color development. Its maximum is situated at 546mμ or somewhat longer wavelengths, shifted distinctly towards the shorter wavelengths from that of the Schiff pigment developed with formaldehyde, as far as the both reactions are conducted according to the standard procedure.
5. Two samples of DNA obtained from beef spleen and herring sperm give fairly identical extinctions per unit quantity of DNA phosphorus.
